'A large crowd of at least a few thousand has turned out – cross country is popular in Kenya'. Photograph: Adharanand Finn

A long line of men stretches out across a dusty football pitch. A few people are rushing along the front of the line, trying to keep order. I'm watching from a distance, so it's hard to see what sets them off, but suddenly half of them are charging across the field towards me. A shout goes up from the crowd as marshals rush onto the pitch to halt the runners. Some of them don't want to stop and have to be virtually pulled to the ground. Eventually they all return to the start line to try again.

We have arrived in Iten in the Rift Valley in Kenya just in time to catch the last leg of the national cross country series. The race pulls in mainly local runners, but here in Iten that means an array of world and Olympic medallists. Competition is stiff, so getting a good start is vital.

The second time, they get it right and the line quickly becomes a swarm of athletes fighting to get ahead. I'm standing next to one of the green-shirted marshals at the first corner. His name is Daniel Komen, the legendary former world champion and multiple world record holder. We watch together as the field arrows towards us and darts around the corner. It is like they are sprinting for their lives, but they still have over seven miles to run, in almost 30C heat.

It may be largely a local competition, but the line-ups here are arguably stronger than at the world cross country championships. At the world cross country there are only six Kenyans in each race – last year in the men's race, five of them finished in the top nine places. Here there are 300 Kenyans in each race. It is quite a sight.

Unlike British races, where you will see a fair sprinkling of grey hair and bandy legs, and many runners who are clearly doing it purely for fun, in Kenya, everyone is under 40 and fast. I briefly contemplated running, but after only two days in Iten, it was a bit too soon.

There is one Briton in the field, however. He trails in just a few places from the back and I'm thinking he is a brave man even to be out there. Later, I find out that his name is Tom Payn and that he was the 4th fastest marathon runner in Britain in 2009. In hindsight, if that's how far behind someone that good is, I would have definitely finished last, by a long way.

A large crowd of at least a few thousand has turned out – cross country is popular in Kenya – and they are treated to four frantic races. The start of the junior boys race is even faster than the senior men's race, while in the women's race, world 5000m silver medallist, Sylvia Kibet, produces a barnstorming sprint at the end – to finish third.

The quality of the running is slightly lost on my children, who enjoy watching, but find it all a bit too hot and a bit too long. My wife initially sits down with them on the front row of a nice marquee someone has put up by the finish. As well as the welcome shade, someone in the tent is handing out free bottles of water. But after a few funny looks and badly disguised coughs we realise we are taking up the prime viewing seats in the VIP tent – seats reserved for the head of the army, the head of the Kenyan Olympic Committee … people like that.

Back out in the late morning heat, my little boy, Ossian, is finding it all too much and in the end Marietta has to take him away for a feed. He may not have seen all the races, but later that day he starts playing a new game. He stands at one end of the large veranda in our hotel and says "ready, steady, go" and then starts running with a big grin on his face. The new David Rudisha? Watch this space …• The book Running with the Kenyans by Adharanand Finn will be published in 2012